Context. Massive spectroscopic survey are becoming trendy in astrophysics and cosmology, as they can address new fundamental knowledge such as Galactic Archaeology and probe the nature of the mysterious Dark Energy. To enable massive spectroscopic surveys, new technology are being developed to place thousands of optical fibers at a given position on a focal plane. These technology needs to be: 1) accurate, with micrometer positional accuracy; 2) fast to minimize overhead; 3) robust to minimize failure; and 4) low cost. In this paper we present the development of a new 8-mm in diameter fiber positionner robot using two 4mm DC-brushless gearmotors, developed in the context of the Dark Energy Spectroscopic Instrument. This development was conducted by a SpanishSwiss (ES-CH) team led by the Instituto de Física Teórica (UAM-CSIC) and the Laboratoire d'Astrophysique (EPFL), in collaboration with the AVS company in Spain and the Faulhaber group (MPS & FAULHABER-MINIMOTOR) in Switzerland. Aims. The meachanical concept, DC-brushless motor properties, and the final performance of a prototyped unit is presented. Methods. Performance and verification tests were conducted with a fiber view camera-based optical set-up and using an automatic algorithm. Results. The prototype build is mechanically robust and reliable, and its control electronics ensure a very firm system with an xy positional accuracy better than 5µm. Conclusions. In this paper, we validate the concept of our advanced 8-mm fiber robot positioner prototype, as well as demonstrate that it can meet the requirements of the DESI project. Such efficient gearmotor fiber positionner robotic system can be adapted to any future massive fiber-fed spectrograph instrument.

MEGARA is an integral-field and multi-object medium-resolution spectrograph for the GTC 10.4m telescope, which was commissioned on June-August 2017. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a Multi-Object Spectrograph (MOS) mode, composed by 92 robotic positioners carrying 7-fiber minibundles each. This paper presents the models and measurements developed for the alignment between the image of the telescope pupil and the 100-µm fiber cores during the integration and verification at the laboratory. On the one hand, the error in the positioner-minibundles assembly was optimized with the aim of achieving a fiber-to-fiber flux homogeneity better than 10%. On the other hand, the positioner pointing was characterized in order to achieve a pointing precision of 1/5 of the spaxel size (which has been designed to be 0.62 arcsec). The on-sky measurements obtained during the commissioning to verify our laboratory results are also presented.

MEGARA is the multi-object medium-resolution spectrograph for the GTC 10m telescope. MEGARA offers two observing modes, the LCB mode, a large central IFU; and a MOS mode composed by 92 robotic positioners carrying 7 fibers minibundles. Microlens are required to fit the GTC f/17 to the f/3 at the fiber entrance, where pupil image is oversized to have a fiber-to-fiber flux variation better than 10%. This tight requirement imposed manufacturing tolerances for the different components and required the development of a gluing station to provide a centering precision better than 5μm. We present the overview of the optical bundles, the gluing station and the final performance obtained during the integration and tests.

MEGARA (Multi Espectrógrafo en GTC de Alta Resolución para Astronomía) is the future optical Integral-Field Unit (IFU) and Multi-Object Spectrograph (MOS) for the 10.4-m Gran Telescopio CANARIAS (GTC). MEGARA has three different fiber bundles, the Large Central Bundle covering 12.5 arcsec × 11.3 arcsec on sky, the Small Compact Bundle, of 8.5 arcsec × 6.7 arcsec, and a Fiber MOS positioner system that is able to place up to 100 mini-bundles with 7 fibers each in MOS configuration within a 3.5 arcmin × 3.5 arcmin FOV. The MEGARA focal plane subsystems are located at one of the GTC Folded Cassegrain focal stations. A field lens provides a telecentric focal plane, where the fibers are located. Micro-lenses arrays couple the telescope beam to the collimator focal ratio at the entrance of the fibers. Finally, the fibers, organized in bundles conducted the light from the focal plane to the pseudo-slit plates at the entrance of the MEGARA spectrograph, which shall be located at one of the Nasmyth platforms. This article also summarizes the prototypes already done and describes the set-up that shall be used to integrate fibers and micro-lens and characterize the fiber bundles.

In these proceedings we give a summary of the characteristics and current status of the MEGARA instrument, the future optical IFU and MOS for the 10.4-m Gran Telescopio Canarias (GTC). MEGARA is being built by a Consortium of public research institutions led by the Universidad Complutense de Madrid (UCM, Spain) that also includes INAOE (Mexico), IAA-CSIC (Spain) and UPM (Spain). The MEGARA IFU includes two different fiber bundles, one called LCB (Large Compact Bundle) with a field-of-view of 12.5×11.3 arcsec 2 and a spaxel size of 0.62 arcsec yielding spectral resolutions between R=6,800-17,000 and another one called SCB (Small Compact Bundle) covering 8.5×6.7 arcsec 2 with hexagonally-shaped and packed 0.42-arcsec spaxels and resolutions R=8,000-20,000. The MOS component allows observing up to 100 targets in 3.5×3.5 arcmin 2 . Both the IFU bundles and the set of 100 robotic positioners of the MOS will be placed at one of the GTC Folded-Cass foci while the spectrographs (one in the case of the MEGARA-Basic concept) will be placed at the Nasmyth platform. On March 2012 MEGARA passed the Preliminary Design Review and its first light is expected to take place at the end of 2015.